1. Field of the Invention
This invention is generally related to the preparation of doped plastics for use in laser operations. In particular, the invention is directed to novel dye doped lasing plastics and the process or controlled doping method for the preparation of dye impregnated laser plastics.
2. Background of the Invention
The use of a solid matrix such as a plastic for dye lasers obviates many of the common problems associated with static or flowing dye systems; e.g., convective schlieren, evaporation, flow fluctuation stagnation films, solvent or dye poisoning, system ruggedness and maintenance, and even explosions.
Prior art methods of producing dye impregnated plastics may generally be characterized as either bulk or solution polymerization methods whereby laser dyes are added to a solution of catalysts and monomers prior to polymerization, or at some point in time before the final polymerization of the monomers into a solid matrix. See for example Oster et al, Luminescence in Plastics Nature, Dec. 15, 1962, p. 1089 and Jones et al, Temperature Effects on the Phosphorescence of Aromatic Hydrocarbons in Poly(methyl-methacrylate), Journal of Chemical Physics, Feb. 1969, p. 1134.
The chemical reactions that take place during these prior art bulk polymerization or solution polymerization processes, the temperature of the reactions, and the changing pH quickly destroy sensitive dyes. Therefore, these prior art processes are suitable for the doping of only a few plastic hosts with a few strong or insensitive laser dyes. The plastic hosts most suited for laser applications are polymethylmethacrylate (PMMA) polymers doped with laser dyes selected from the Rhodamine dye family because of the lasing efficiency exhibited by these dyes and the excellent stability exhibited by the host plastic. These materials when pumped by a pulsed high peak power pumping laser are suitable for lasing actions in the 0.55 to 0.62 micron wavelength range. Other dyes having electro-chemical properties suitable for use as a high efficiency doped lasing medium at longer wavelengths such as Carbazine 122 and Cresyl Violet are attacked by the prior art processes for incorporating them into suitable plastic hosts.
For fieldable laser applications, it is desirable to utilize solid laser mediums capable of lasing in a wide wavelengths range. Transparent polymethylmethacrylate impregnated with specific laser dyes have been shown to be a useful laser medium at specific wavelengths. See B. H. Soffer et al, "Continuously Tunable Narrow Band Organic Dye Laser," Appl. Phys. Ltr., Vol. 10, pp. 266-267 (1967). However, in order to obtain lasing actions over a wider wavelength region, additional dyes must be employed. The utilization of these dyes has been precluded by the inability to incorporate them into the plastic host, using prior art methods, without altering the dye characteristics. The dyes are either destroyed during the bulk process or they undergo a major change in their lasing character.
Prior art methods for the preparation of dye impregnated plastics exhibit the additional disadvantage, because of their bulk process nature, of producing dye impregnated plastics having uniformly distributed dye molecules throughout the host medium. This feature leads to exponential gain and index of refraction profiles when the medium is transversely pumped because of the exponential absorption of laser pumping energies.
Therefore, one purpose of this invention is to provide a dye impregnated plastic suitable for use as a lasing material that will yield a flat gain and index of refraction profile when pumped transversely.
A second purpose of this invention is to provide a dye impregnated plastic medium that lases at frequencies above 0.620 microns.
A further purpose of this invention is to provide a process for doping plastic host materials with sensitive laser dyes.
A still further purpose of this invention is to provide a process for selectively varying the dye concentration throughout a dye impregnated plastic medium.